Don't like codec packs
they can bork your system quite easily
Installing multiple versions of the same codec
Dodgy priority values, etc.

I'm a great fan of ffdshow
http://ffdshow-tryout.sourceforge.net

It's a front end to all DirectShow filters installed on your system
and is a great way to "chain" the different filters in the way that you want

You want 5.1 audio piped directly to your surround sound system untouched via S/PDIF, but stereo sound decoded to analogue and routed to your desktop speakers?
Fine, just tell ffdshow to do that, and it's done

You want standard resolution 4:3 video stretched horizontally to fit your widescreen TV
but don't want 16:9 to be touched at all?
Fine, just tell ffdshow to do that, and it's done

Plus it now has native support for mpeg2 DVD decoding (so no need to pay for proprietary codecs from winDVD or powerDVD or whoever)

Uninstall all your horrible codec packs and proprietary filters and replace with one

Any media player that supports directshow (Windows media player included) will follow your settings, and play all your media the way you want it played

sweet bliss